CONSTRAINING UPLIFT HISTORY OF THE SANTA SUSANA MOUNTAINS, WESTERN TRANSVERSE RANGES, SOUTHERN CALIFORNIA THROUGH U-PB DETRITAL ZIRCON GEOCHRONOLOGY

The Santa Susana fault (SSF) is the western extension of the Sierra Madre fault system, an east- west trending reverse fault system in the Transverse Ranges. Slip on the SSF and related faults was associated with growth of the Santa Susana Mountains which form the southern boundary of the Ventura basin. The Saugus Formation in the footwall of the SSF is poorly lithified Pleistocene strata. The Saugus Formation in the SSF footwall was cut off from source areas to the north by slip on the SSF and uplift of the mountains. Previous studies estimated uplift to have initiated between 2.3-0.7 Ma through paleomagnetic dating and upsection changes in clast provenance, yielding a geologic slip rate of 5.9 ±3.9 mm/yr. This study utilized detrital zircon geochronology and sandstone modal compositions to build upon previous clast-count provenance studies to examine the provenance of the Saugus Fm. and refine the timing of uplift of the Santa Susana Mountains.

Samples were collected from a stratigraphic transect through the Saugus Formation, as well as from the middle Saugus Formation at two locations along strike. Additional samples were collected from the Neogene units exposed in the hanging wall of the SSF. U-Pb detrital zircon geochronology reveals distinctive upsection trends in the detrital zircon spectra of the Neogene and Quaternary samples. Across the transition from the lower marine to the middle non-marine members of the Saugus Formation, there is a shift to similar provenance with the upper Neogene units in the SSF hanging wall. This indicates that the SSF hanging wall was a local source of sediment by ~1.1 Ma. Work in progress includes analysis of modal composition through the Saugus Formation and SSF hanging wall strata, as well as developing models for structural growth of the SSF and sedimentation. Once complete, a better estimation of the long-term slip rate of the fault over the Quaternary can be made, in addition to providing insight on sediment dispersal trends during Cenozoic deformation in the western Transverse Ranges.